He that loveth his brother abideth in the light - Has true religion, and enjoys it.
And there is none occasion of stumbling in him - Margin, "scandal." Greek, "and there is no stumbling" (or scandal - σκάνδαλον skandalon - in him.) The word here used, means anything against which one strikes or stumbles; and then a stumbling-block, an impediment, or anything which occasions a fall. Then it is used in a moral or spiritual sense, as denoting that which is the occasion of falling into sin. See the Matthew 5:29 note, and Romans 14:13 note. Here it refers to an individual in respect to his treatment of others, and means that there is nothing, so far as he is concerned, to lead him into sin. - Robinson, Lexicon. If he has love to the brethren, he has true religion; and there is, so far as the influence of this shall extend, nothing that will be the occasion of his falling into sin in his conduct toward them, for "love worketh no ill to his neighbor," Romans 13:10. His course will be just, and upright, and benevolent. He will have no envy toward them in their prosperity, and will not be disposed to detract from their reputation in adversity; he will have no feelings of exultation when they fall, and will not be disposed to take advantage of their misfortunes; and, loving them as brethren, he will be in no respect under temptation to do them wrong. In the bosom of one who loves his brother, the baleful passions of envy, malice, hatred, and uncharitableness, can have no place. At the same time, this love of the brethren would have an important effect on his whole Christian life and walk, for there are few things that will have more influence on a man's character in keeping him from doing wrong, than the love of the good and the pure. He who truly loves good people, will not be likely in any respect to go astray from the paths of virtue.

He that loveth his brother - That is, his neighbor, his fellow creature, whether Jew or Gentile, so as to bear him continual good will, and to be ready to do him every kind office; abideth in the light - not only gives proof that he has received Christ Jesus the Lord, but that he walks in him, that he retains the grace of his justification, and grows therein.
And there is none occasion of stumbling in him - Και σκανδαλον εν αυτῳ ουκ εστιν· And there is no stumbling block in him; he neither gives nor receives offense: love prevents him from giving any to his neighbor; and love prevents him from receiving any from his neighbor, because it leads him to put the best construction on every thing. Besides, as he walks in the light, he sees the stumbling blocks that are in the way, and avoids them; every part of his path being illuminated. Many fall into sin because they do not see the snares that are in the way; and they do not see the snares because they either have not received, or do not abide in, the light.

He that loveth his brother,.... As such, and because he is his brother in Christ, and that cordially and sincerely, without hypocrisy and dissimulation, and by love serves him, both in things temporal and spiritual, and so observes the new, and yet old commandment,
abideth in the light: it is a plain case, that such a man is in the light of grace, and continues in it; for though it is not his love to the brethren which is the cause of his light, of his being and continuing in it, for that is owing to the spirit of light and knowledge, but on the contrary, light is the cause of his love; yet it is an evidence of it, that by which it is known, as the cause is known by the effect; see John 3:14;
and there is none occasion of stumbling in him, or "there is no scandal" or "offence in him"; he gives no offence to his brother, or at least, as much as in him lies, he takes care that he gives none; he avoids, as much as can be, putting a stumblingblock, or an occasion to fall, in his brother's way, by the use of things indifferent, or by any other action; nor will he easily take offence at what is said or done unto him, for charity or love is not easily provoked, it suffers long, and bears all things; see 1-Corinthians 13:4; nor does he so much and so frequently transgress the laws of God, and particularly those which regard his neighbour or his brother, and so easily fall into the snares of Satan, because he is in the light, and walks in the light, and sees his way, and what lies in his way, and, so shuns and avoids occasion of stumbling and falling. There is not in him that wrath, and malice, and envy, which lead on to the commission of other sins; for love works no ill, but fulfils the law, and will not suffer him to commit adultery, to kill, to steal, or bear false witness against his neighbour, friend, and brother; see Romans 13:9; and such an one enjoys great peace, tranquillity, and happiness; he has much comfort in himself, and pleasure in the saints, and delight in their company; he walks inoffensively, and in an harmless manner, without hurting himself, or any other, Psalm 119:165.

Abiding in love is abiding in the light; for the Gospel light not only illumines the understanding, but warms the heart into love.
none occasion of stumbling--In contrast to, "He that hateth his brother is in darkness, and walketh in darkness, and knoweth not whither he goeth, because that darkness hath blinded his eyes." "In him who loves there is neither blindness nor occasion of stumbling [to himself]: in him who does not love, there is both blindness and occasion of stumbling. He who hates his brother, is both a stumbling-block to himself, and stumbles against himself and everything within and without; he who loves has an unimpeded path" [BENGEL]. John has in mind Jesus' words, John 11:9-10. ALFORD well says, "The light and the darkness are within ourselves; admitted into us by the eye, whose singleness fills the whole body with light."

He that loveth his brother - For Christ's sake. Abideth in the light - Of God. And there is no occasion of stumbling in him - Whereas he that hates his brother is an occasion of stumbling to himself. He stumbles against himself, and against all things within and without; while he that loves his brother, has a free, disencumbered journey.